I am assuming the schema of all these files is same

If so how to process it depends what your comfortable with

The steps that come to mind are

• In the landing zone have a folder structure per client
• read all the parquet contract files into delta input_file_name() may be useful to know which file your processing

(Contracts are per client with a type and start end date)

• Create a column for client name

Perform aggregations

• how many different contract did the client have

---group by clientname and a count

• of which type

--group by clientname and distinct count on type

• when was the dateof the first contract

--group by clientname and min date

• and the last contract

--group by clientname and max date

• how long have we been working with him.

--difference between min and max